The present invention relates to a binocular that has a hand-vibration compensation system.
Recently, binoculars provided with hand-vibration compensation systems for preventing vibrations of an observed image due to hand-vibration of a user have been developed.
A binocular is provided with a pair of telescopic optical systems arranged side by side. Each of the systems comprises an objective lens, an erecting system such as a Porro prism and an eyepiece. In one type of the hand-vibration compensation systems, compensation optical elements are arranged in the telescopic optical systems. The compensation optical elements are driven by a driving mechanism. Since moving of the compensation optical element changes a direction in which a light beam proceeds, the movement of the compensation optical element moves the image in the user view. In the other words, when the image is moved by the hand-vibration, the compensation optical element is driven to move the image so that it is observed as if it stays at the same position, thus the image vibration can be compensated.
A compensation lens may be used as the compensation optical element. At the given position of the compensation lens, moving amount of the image due to the decentering of the compensation lens depends on the decentering amount and a refractive power of the compensation lens. The larger the refractive power is or the larger the decentering amount is, the larger the moving amount of the image is.
Since the refractive power is limited to reduce aberrations, a movable range of the compensation lens becomes relatively large to obtain a sufficient effect of the hand-vibration compensation in the conventional hand-vibration compensation system. This results problems of increased size of a binocular casing and of lowered response in driving of the compensation lenses.